1. Field of the Invention
The present invention relates generally to an absorbent composition for absorbent articles such as diapers, incontinence products, training pants, sanitary napkins, and the like. In particular, the present invention relates to an absorbent article that has good strikethrough and rewet properties.
2. Description of Related Art
Disposable absorbent articles typically include a moisture-impervious backing sheet, an absorbent pad, and a liner sheet that contacts the body of a person wearing the article. In addition, elasticized regions are provided around the edges of the article to secure the article about the waist and legs of a wearer. Absorbent articles such as diapers typically further comprise opposed front and rear waist portions defining a waist opening, a crotch portion disposed there between, and a pair of elastically contractible leg openings along the side edges of the crotch portion. Disposable diapers having elasticized margins for placement about the legs of a wearer are disclosed in U.S. Pat. No. 4,050,462 and U.S. Pat. No. 5,092,861, the disclosures of which are incorporated by reference herein in their entirety. An absorbent article having elasticized side margins and waist band margins are described in U.S. Pat. No. 4,300,562, the disclosure of which is incorporated by reference herein in their entirety.
Despite previous advancements in the field of absorbent articles, there still is a current need to provide absorbent articles that are better able to contain urinary and fecal excretions. For instance, problems with prior diaper designs include inferior absorbency and leakage of urinary or fecal material from the article. Prolonged contact of liquid or semi-solid excreta with the skin of the wearer is also a continuing problem. For example, the moisture vapor and heat generated by the bodily exudate trapped within a diaper may lead to conditions adjacent to the wearer's skin that promotes skin irritation, infection, and the like.
Developing highly absorbent articles for use as disposable diapers, adult incontinence pads and briefs, and catamenial products such as sanitary napkins typically entails developing relatively absorbent cores or structures that can acquire, distribute and store large quantities of discharged body fluids, in particular urine. For example, absorbent structures include particulate absorbent polymers often referred to as “hydrogels,” “superabsorbents” or “hydrocolloid” materials. See, for example, U.S. Pat. No. 3,699,103, and U.S. Pat. No. 3,770,731 that disclose the use of such particulate absorbent polymers in absorbent articles. Indeed, the development of high performance diapers has been due in part to thinner absorbent cores that take advantage of the ability of these particulate absorbent polymers to absorb large quantities of discharged aqueous body fluids, typically when used in combination with a fibrous matrix. See, for example, U.S. Pat. No. 4,673,402 and U.S. Pat. No. 4,935,022, that disclose dual-layer core structures comprising a fibrous matrix and particulate absorbent polymers useful in fashioning high performance diapers.
Other absorbent materials capable of providing good absorbency and good capillary fluid transport are open-celled polymeric foams. Certain types of polymeric foams have been used in absorbent articles for the purpose of imbibing, and/or wicking aqueous body fluids. See, for example, U.S. Pat. No. 3,563,243 (absorbent pad for diapers and the like where the primary absorbent is a hydrophilic polyurethane foam sheet); U.S. Pat. No. 4,554,297 (body fluid absorbing cellular polymers that can be used in diapers or catamenial products); U.S. Pat. No. 4,740,520 (absorbent composite structure such as diapers, feminine care products and the like that contain sponge absorbents made from certain types of super-wicking, crosslinked polyurethane foams).
There are a number of documents describing absorbent foams, for example, those that have been made from High internal Phase Emulsions (hereafter referred to as “HIPE”), or those made from hydrophilic, flexible, open-celled foam such as a melamine-formaldehyde foam (e.g., BASOTECT™ made by BASF). See, for example, U.S. Pat. Nos. 5,147,345, 5,260,345, 5,268,224, 5,318,554, 5,331,015, 5,352,711, 5,550,167, 5,632,737, 5,692,939, 5,786,395, and 5,851,648. Some of these foams provide desirable fluid handling properties, including: (a) relatively good wicking and fluid distribution characteristics to transport the imbibed urine or other body fluid away from the initial impingement zone and into the unused balance of the foam structure to allow for subsequent gushes of fluid to be accommodated; and (b) a relatively high storage capacity with a relatively high fluid capacity under load, i.e. under compressive forces. These HIPE absorbent foams are also sufficiently flexible and soft so as to provide a high degree of comfort to the wearer of the absorbent article; some can be made relatively thin until subsequently wetted by the absorbed body fluid.
U.S. Pat. Nos. 5,147,345, and 5,310,554 to Young et al. discloses absorbent articles, such as diapers, for the management of incontinence. Such articles utilize in their absorbent cores a fluid acquisition/distribution component and a fluid storage/redistribution component maintained in fluid communication with the acquisition/distribution component. The fluid acquisition/distribution component can be any porous hydrophilic, e.g., fibrous or foam-based, material which will provide an initial Fluid Acquisition Rate of at least 2 mL of synthetic urine per second and will also preferably provide a 30-minute Vertical Wicking Height of at least 2 cm. The fluid storage/redistribution component comprises a hydrophilic, flexible, open-celled polymeric foam having a free absorbent capacity of at least about 12 mL of synthetic urine per gram of dry foam and an absorbent capacity under a 5.1 kPa confining pressure which is at least 5% of this free capacity. Preferred fluid acquisition/distribution component materials comprise chemically stiffened, twisted, curled cellulosic fibers. Preferred fluid storage/redistribution component materials comprise absorbent foams prepared by polymerizing a high internal phase emulsion (HIPE).
U.S. Pat. Nos. 5,268,224, and 5,331,015 to Des Marais et al. discloses absorbent foam materials suitable for use as or in the absorbent cores of absorbent articles, such as diapers which absorb and retain aqueous body fluids. Such foam materials comprise hydrophilic, flexible open-celled structures which are preferably prepared by polymerizing high internal phase (HIPE) water-in-oil emulsions. Such foam materials have a pore volume of from about 12 to 100 mL/g, and a capillary suction specific surface area of from about 0.5 to 5.0 m2/g. These materials also exhibit a resistance to compression deflection such that a confining pressure of 5.1 kPa produces after 15 minutes a strain of from about 5% to 95% compression when the material is saturated at 37° Celsius to its free absorbent capacity with synthetic urine.
U.S. Pat. Nos. 5,851,648, 5,786,396, 5,632,737, 5,692,939, and 5,550,167 disclose absorbent foams materials that are capable of acquiring and distributing aqueous fluids, especially discharged body fluids such as urine. These absorbent foams combine relatively high capillary absorption pressures and capacity-per-weight properties that allow them to acquire fluid, with or without the aid of gravity. These absorbent foams are alleged to give up this fluid to higher absorption pressure storage materials, including foam-based absorbent fluid storage components, without collapsing. These absorbent foams are made by polymerizing high internal phase emulsions (HIPEs).
U.S. Pat. No. 5,352,711 to Des Marais discloses that normally hydrophobic foams and polymerized water-in-oil emulsion foams are rendered hydrophilic by means of treatment with simple surfactants and hydrophilizing agent salts. Thus, a surfactant-containing foam is treated with a solution of, for example, calcium chloride, and is dried to leave a substantially uniformly distributed residue of hydrated or hydratable calcium chloride on the surfactant-containing internal foam surfaces. In-use, the combination of surfactant and calcium chloride hydrate provides a hydrophilic surface to the foam. Other hydratable calcium or magnesium salts such as magnesium chloride can be used. The resulting hydrophilized foams are said to be suitable for use in absorbent devices, including diapers, sanitary napkins, bandages, and the like.
Polyurethane foams are known to be useful as absorbent materials. For example, U.S. Pat. No. 5,164,421 discloses a hydrophilic foam that is applicable for the manufacture of absorptive devices. The hydrophilic polyurethane foams can be made from aromatic polyisocyanates.
A desirable feature of absorbent articles is that they should exhibit good strikethrough and low rewet characteristics, permitting bodily discharges to rapidly penetrate there through, but not flow back through to the skin of the wearer. Rewet has many causes. Typically, rewet occurs when the absorbent core of the article becomes saturated and unable to hold more fluid. Rewet also occurs when the absorbent core is below its saturation point. For example, rewet may occur when the absorbent core can not absorb a given volume of fluid quickly enough. Rewet also may occur when an absorbent article is placed under pressure, causing fluid to be mechanically forced out of the absorbent core. Typically, when an absorbent article is at a high saturation level or at the saturation point, rewet becomes an increased problem, as the compressive force required to force fluid out of the absorbent core decreases.
One suggested solution to reduce the rewet characteristics of absorbent articles is to provide an acquisition or transport layer between the absorbent core and the liquid permeable body contacting layer (e.g., topsheet). The acquisition layer distributes fluids across the surface of the absorbent core to improve the absorbent core's ability to rapidly absorb fluids. Once the fluids are absorbed by the core, the acquisition layer acts as a relatively dry boundary between the topsheet and the absorbent core to prevent rewet. This benefit is minimal, however, because conventional acquisition layers do not prevent fluid from reemerging from the core when the core is placed under pressure, especially when the core is at or near the saturation point. Rewet therefore typically occurs under these circumstances.
Another suggested solution is to provide an apertured film layer to prevent backflow of fluid out of the absorbent core. Apertured films having three-dimensional funnels have been found to provide preferential fluid flow away from the surface of the film and through the funnels. Such films may provide beneficial rewet capabilities when properly employed in the construction of an absorbent article. U.S. Pat. No. 6,171,291, issued to Palumbo et al., discloses the use of an apertured film body-contacting topsheet to prevent rewet. It has been recognized, however, that the use of an apertured film as a topsheet may necessitate careful selection of or additional modifications to the apertured film to provide the apertured film with a suitable feel and texture for use as a body-contacting surface. These and other considerations significantly increase the cost of the article, and/or reduce design flexibility.
An apertured layer may also be used as a rewet barrier located between the topsheet and the absorbent core. U.S. Pat. No. 5,603,707, issued to Trombetta, et al., discloses an absorbent article having a macroscopically expanded apertured web acting as a rewet barrier disposed between the absorbent core and an additional fibrous acquisition layer located adjacent the topsheet. U.S. Pat. No. 4,323,069, issued to Ahr et al., also discloses an intermediate layer comprising capillary openings, located between a fibrous acquisition layer and an absorbent core. U.S. Pat. No. 5,352,217, issued to Curro, discloses the use of multiple layers of apertured film topsheets to reduce rewet.
It is desirable to provide cost-efficient absorbent articles that display superior absorbency, as well as novel compositions and composites for use in the absorbent articles. Further, it is desirable to provide a cost-efficient process for producing absorbent articles having superior absorbency. It is worth noting here, that even despite the aforementioned disadvantages, nothing stated herein detracts from the usefulness or possibility that any of these materials may be used in conjunction with the present invention.
The documents described above are incorporated herein by reference in their entirety.